The present invention relates generally to a method for writing servo code into a magnetic disk drive and, more particularly, to a method for writing servo code into a magnetic hard disk drive (HDD).
There is always a trend in the development of the magnetic disk drive to try to increase the storage capacity of a magnetic hard disk drive. One way to achieve the aim is to increase the track density of the disk drive. The track density of a modern, high performance HDD has been up to more than 1000 TPI (Tracks Per Inch) while the width of each track is less than one mil. To meet the requirement of the high track density in a magnetic disk drive which has a stepper motor to serve as a magnetic head actuator, a closed loop servo control technique must be used in association with the stepper motor to carry out a track positioning operation. In a closed loop servo control procedure, a servo code prestored in a predetermined region on a magnetic disk of the HDD is read out and serves as a reference source. The servo code read out provides information with regard to the quantity of off-track according to which a stepper motor controlling circuit carries out a micro-stepping regulation operation to determine the position of a track. Therefore, it is absolutely important that the servo code is recorded on a magnetic disk with an even track spacing. The tracks obtained on each disk surface according to an unevenly spaced servo code will be unevenly disposed. As a result, the validity of the data stored on disks and the performance of magnetic disk drives will be greatly affected.
In the production of a magnetic disk drive, two kinds of methods have been adopted to give a magnetic disk drive with a servo code which is accurately and evenly spaced. One method uses a dedicated servo code writing apparatus incorporating a laser positioning system to write a servo code into each magnetic disk drive on a one-by-one basis. Since expensive equipment is needed, the cost to produce a magnetic disk drive by using this method is very high. The other method involves accurately measuring the relationship between the operating current of the stepper motor in a disk drive and the micro-step spacing to figure out an operating current which is needed to obtain evenly spaced steps, and using the operating current figured out to drive the stepper motor in an opened loop manner so as to write the servo code into a magnetic disk of the disk drive. Although the production procedure by using the latter method identified above is simple, a great deal of time is needed in the development process to analyze the relationship between the step spacing and the operating current of a stepper motor. Furthermore, because of the differences which inevitably exist between the properties and the assembly tolerance of each stepper motor and each magnetic head carriage, only a fair result may be obtained by using the latter method. It is still impossible to achieve a smooth production with a high yield rate and a high quality.